1. Technical Field
The embodiments described herein generally relate to a system and method for a vehicle-dynamics control architecture in hybrid electric vehicles (HEVs).
2. Background Art
Prior attempts at vehicle-dynamics control have tended to be modular in that a modular control approach allows for the reuse of controllers across various vehicles so that only calibration adjustments need to be made to each controller. The modular vehicle-dynamics control generally issues vehicle level fast wheel torque requests for vehicle-dynamics related systems. Such systems include an anti-locking braking system (ABS), traction control (TC) system, an electric stability control (ESC) system, an integrated vehicle-dynamics (IVD), etc. However, such requests are generated based on a prior knowledge of both system approximate wheel torque response dynamic capability (such as bandwidth or time constant) and the range of authority (positive and negative deltas). The approximated nature of the capabilities sometimes renders the vehicle-dynamics control less capable than physically possible, particularly for vehicles with multiple torque actuators having different dynamic capability and a range of authority with a time-varying split or distribution in use of the actuators.
FIG. 1 depicts a conventional vehicle-dynamics control system 10 that is based on the modular control approach. The system 10 includes a vehicle layer 12, a coordination layer 14 and a plurality of torque generating devices 15. The vehicle layer 12 contains functions related to the supervision of the control and coordination of all motions of the vehicle body. Such motions of the vehicle body may include all six degrees-of-freedom (DOF) of the vehicle body, as well as the sensing and interpreting of vehicle-related quantities. The central decision operating process of the vehicle-dynamic control resides in the vehicle layer 12. The central decision operating process determines the applicable amount of force that may have to be applied to the vehicle as a whole, in order to satisfy the overall intended behavior within physical limits. The coordination layer 14 contains coordinators that independently control and coordinate respective actuators within the torque generating devices 15. The task of the coordination layer 14 is to determine how wheel torque requests from the vehicle layer 12 are to be realized by the subsystems/actuators which belong to torque generating devices 15. The coordinator layer 14 may also provide feedback on the vehicle state to the driver.
The vehicle layer 12 receives a signal DRV_TQ_REQ. The signal DRV_TQ_REQ corresponds to an amount of torque that is needed to satisfy the amount of torque being requested by the driver as the driver operates the vehicle. The vehicle layer 12 includes a vehicle-dynamics controller (VDC) 16. The VDC 16 may be implemented as a standalone controller and generally controls various vehicle-dynamics attributes. Such attributes may include but are not limited attributes associated with an anti-locking brake system (ABS), traction control (TC) system, electronic stability control (ESC) (an integrated vehicle-dynamics IVD system) and a roll stability control (RSC) system. The ABS generally prevents the wheels from locking up as the vehicle undergoes a braking event. The TC system generally reduces power to drive wheels of the vehicle in order to minimize wheel-spin and maximize traction. The ESC or IVD system generally performs yaw stability control whereby the vehicle's motion of rotation about a vertical axis is controlled. The RSC system controls the motion of the vehicle by selectively applying brakes and adjusting the speed of the vehicle to prevent the vehicle from rolling over. The VDC 16 may be reused or implemented to support a plurality of vehicle lines and/or programs.
The coordination layer 14 includes a torque-distribution module 18. The coordination layer 14 generally corresponds to hardware characteristics that are specific to a single vehicle program. The torque-distribution module 18 may be configured to transmit/receive signals to/from the vehicle layer 12. The coordination layer 14 further controls various actuators within the torque generating devices 15. The torque generating devices 15 may be generally defined as any component, subsystem, and/or actuator in the vehicle that is adapted to generate torque, which contributes to vehicle traction torque. The torque generating devices 15 includes an engine subsystem 20, a plurality of electrical subsystems 22a-22n and a brake subsystem 24. The engine subsystem 20 generally includes an internal combustion engine of a HEV and one or more engine controllers. The engine controllers are adapted to control the operation of the engine and control the amount of torque generated by the engine. The electrical subsystems 22a-22n each generally include electrically based motors/generators (not shown) and motor/generator controllers for controlling the amount of torque generated by the motor/generator.
In general, the engine and the motor/generators may be defined as active torque actuators. An active torque actuator is indicative of a type of actuator that adds energy to the system. For example, the engine subsystem 20 adds energy by extracting the chemical potential energy in fuel. The electrical subsystems 22a-22n each add energy into the system 10 by extracting the chemical potential energy of the battery. A passive torque actuator such as the brake subsystem 24 is indicative of a type of actuator that may not add energy to the system. Such a passive actuator absorbs energy from the system. For example, friction brakes absorb kinetic energy from a system and convert kinetic energy into heat.
The VDC 16 is adapted to transmit a signal ARB_TQ_REQ to the torque-distribution module 18. The signal ARB_TQ_REQ generally corresponds to an arbitrated torque request that is based on the amount of torque desired by the driver and on the amount of torque requested by the various vehicle-dynamics systems in the vehicle. The VDC 16 is adapted to transmit a signal BRAKE_TQ_REQ to the brake subsystem 24. The signal BRAKE_TQ_REQ corresponds to a net wheel torque requested from the friction brakes which provides braking power beyond powertrain capability and with additional degrees of freedom or channels not conventionally available to powertrain braking (i.e., independent control of 4 wheels).
The torque-distribution module 18 transmits a plurality of control signals (e.g., CTR_ENG, and CTR_A-CTR_N) to the subsystems 20 and 22a-22n of the torque generating devices 15, respectively. The signal CTR_A generally corresponds to the amount of torque that is needed to be produced by the engine subsystem 20. The signals CTR_A-CTR_N generally correspond to the amount of torque that is needed to be produced by the electrical subsystems 22a-22n. The torque-distribution module 18 is configured to control the engine subsystem 20 and the electrical subsystems 22a-22n to produce the desired amount of torque as requested by the VDC 16 while balancing driver traction demand, battery charge maintenance, and fuel economy attributes. As such, the torque-distribution module 18 may vary the amount of torque generated between the engine subsystem 20 and the electrical subsystems 22a-22n in order to achieve desired driver traction demand, battery charge maintenance, and the highest level of fuel economy.
Due to concerns related to fuel economy, if needed, the torque-distribution module 18 may control the engine subsystem 20 to generate the entire amount of torque needed to meet the desired amount of torque as specified on the signal ARB_TQ_REQ. In such a case, the electrical subsystems 22a-22n may not be controlled to generate torque. Additionally, the torque-distribution module 18 may control one or more of the electrical subsystems 22a-22n to generate the entire amount of torque needed as indicated by the signal ARB_TQ_REQ. In such a case, the engine subsystem 20 may remain idle and is in a non-torque producing state. In yet another example, the torque-distribution module 18 may control the engine subsystem 20 and any one or more of the electrical subsystems 22a-22n to produce the desired amount of torque simultaneously if such a condition may yield optimal fuel economy while at the same time meet the desired amount of torque requested by the VDC 16.
The engine subsystem 20 transmits a feedback signal FB_ENG to the torque-distribution module 18. The signal FB_ENG may include a value (e.g., TAU_ENGINE) which generally corresponds to the actual response time of the engine subsystem 20 while attempting to achieve the desired amount of torque as indicated in the signal CTR_ENG from the torque-distribution module 18. The feedback signal FB_ENG also includes values MIN_TQ_ENG and MAX_TQ_ENG which correspond to minimum and maximum torque values, respectively, generated by the engine subsystem 20 in response to the signal CTR_ENG. The electrical subsystems 22a-22n are generally configured to transmit feedback signals FB_A-FB_N to the torque-distribution module 18. The signals FB-A-FB_N includes values TAU_ELEC_A-TAU_ELEC_N, respectively, which correspond to the actual response time for each electrical subsystem 22a-22n while attempting to achieve the desired amount of torque transmitted in the signal CTR_A-CTR_N from the torque-distribution module 18.
The feedback signals FB_A-FB_N also include values MIN_TQ_ELEC_A-MIN_TQ_ELEC_N and values MAX_TQ_ELEC_A-MAX_TQ_ELEC_N. The values MIN_TQ_ELEC_A-MIN_TQ_ELEC_N correspond to the minimum torque valve generated by each electrical subsystem 22a-22n in response to the signals CTR_A-CTR_N. The signals MAX_TQ_ELEC_A-MAX_TQ_ELEC_N correspond to the maximum torque values generated by each electrical subsystem 22a-22n in response to the signals CTR_A-CTR_N.
In general, the engine subsystem 20 and the electrical subsystems 22a-22n are constructed with various limitations and may generate torque that is within a first predetermined range of the amount of torque requested by the VDC 16. Such limitations may be attributed due to hardware capabilities of the engine and electrical subsystems 20 and 22a-22n. Typically, the torque capability of the engine subsystem 20 and the electrical subsystems 22a-22n are a function of battery voltage, state of charge of the battery and/or various torque actuator speed states (e.g., actuators in the engine and electrical subsystems 20 and 22a-22n). The torque, battery voltage, state of charge, and the actuator speed status may prevent the engine and the electrical subsystems 20 and 22a-22n from generating the needed amount of torque as requested by the VDC 16.
The engine subsystem 20 transmits the values MIN_TQ_ENG and MAX_TQ_ENG to the torque-distribution module 18 via the signal FB_ENG. The electrical subsystems 22a-22n transmits the values MIN_TQ_ELEC_A-MIN_TQ_ELEC_N and the signals MAX_TQ_ELEC_A-MAX_TQ_ELEC_N via the signals FB_A-FB_N to the torque-distribution module 18. The torque-distribution module 18 transmits a signal TAU_ACTUAL, a signal MIN_ACTUAL and a signal MAX_ACTUAL to the VDC 16.
In general, the signals TAU_ACTUAL, MIN_ACTUAL, and MAX_ACTUAL provide actual information of the response time to reach the minimum and maximum torque, the minimum torque amount, and the maximum torque amount, respectively, that is established with the torque generating devices 15. In some cases, the torque generating devices 15 may not achieve the desired torque amount as requested by the VDC 16. The VDC 16 uses the signals TAU_ACTUAL, MIN_ACTUAL, and MAX_ACTUAL as feedback signals to modify the desired torque amount (e.g., signal ARB_TQ_REQ) based on new desired torque level commands that may be necessitated due to torque requirements established by the driver and/or the vehicle-dynamics systems of the vehicle.
The system 10 generally provides for a modular focused control architecture which lends itself for providing a common implementation for a number of different vehicle applications. The engine subsystem 20 generally provides for a slower response time in generating torque than the response time of the electrical subsystems 22a-22n. The desired amount of torque needed for the vehicle-dynamics capability of the system 10 is generally limited to the response of the slowest torque actuator which in this case may be the engine subsystem 20. Such a characteristic provides for a limitation in performing vehicle-dynamics control.